
How about airplane kidnapping kinda "pay 1/2 aircraft value or we will destroy it"?
You can't control the plane (it will fly around, not land, you can't send it to depot etc)
If you pay, plane flies to your closest airport, unloads, and you can steer it again
If you won't pay 3 weeks plane will explode in air (then gray wreck will fall to the ground, explode there again and disappear.
Alt versio (not so bloody) - plane flies to edge of map and flies outof camera view

Oh, next disaster: bus crashes: both busses magically meet, break down, then both must go to depot with small speed. Simple, but you will loose profit (profit depens on distance and transport time).
That should be frequent disaster

And I've got question: what does submarine does? Destroys ships?